The proposed research has as its overall objective the enhanced clarification of the structural, electronic, redox, and chemical reactivity properties of the active sites of iron-sulfur proteins (rubredoxins, ferredoxins), one of the two most significant general classes of electron-transfer molecules in biology. With well characterized synthetic analogs (Fe(SR)4) negative, (Fe2S2(SR)4)2 negative, and (Fe4S4(SR)4)2 negative in hand, new research will utilize these species and related proteins in investigations of the following matters, all of which pertain to protein oxidation levels detected in vitro and of doubtless significance in vivo: physical manifestations of the proposed entatic state of rubredoxins; structural and other characterization of oxidation levels previously incompletely defined for both analogs and proteins; possible pathways and kinetics of electron transfer to analog Fe-S centers using initially inner-sphere reductants; kinetics and mechanism of dimer-tetramer analog core conversion; preparation and characterization of the fundamental core cations (Fe2S2)2 positive and (Fe4S4)2 positive of protein sites; dependence of redox potential on ligand structure as varied from simple oraganic groups through native protein fragments to holoproteins; development of the active site core extrusion method to identification of active site structures in more complicated Fe-S proteins and enzymes; development of nonheme mono- and/or dioxygenase activity in synthetic systems using as initial enzyme site simulators (Fe(SR)4) negative and (Fe2S2(SR)4)2 negative, with particular emphasis on dioxygenase substrate transformation. By these studies it is hoped to contribute to a more secure and thorough interpretation of the physical and chemical reactivity properties of the active sites of Fe-S proteins and enzymes, with the three types of synthetic analogs serving as excellent representations of these sites unperturbed by protein structure and environment.